1. Field of the Invention
The present invention relates to processes for iodinating aromatic compounds and to processes for partially separating the reaction products.
2. Discussion of the Background
It has long been desired to be able to derivitize aromatic compounds and in particular condensed ring aromatic compounds in commercially attractive quantities since many of these compounds possess properties which would fill long-sought needs. In particular, substituted benzene and naphthalene carboxylic acids or esters are particularly desired for use in the manufacture of polyesters which would have excellent properties when fabricated into films, bottles or coatings. However, techniques for producing these carboxylic acids and esters are very expensive and impractical for commercial exploitation.
Also commercially important are poly(arylene sulfide) resins which are thermosetting-thermoplastic polymer materials with good thermal stability, unusual insolubility, resistance to chemical environments and inherent flame resistance. Poly(arylene sulfide) resins are useful for applications such as coatings for pipes, tanks, pumps and other equipment.
Halogenated aromatic compounds provide a convenient feedstock material for the preparation of both aromatic polyesters and poly(arylene sulfide) resins. Iodoaromatic compounds, and in particular, monoiodoaromatic and diiodoaromatic compounds provide a common starting material from which to produce polyesters and poly(arylene sulfide) resins.
Synthesis of iodobenzene starting from benzene and iodine is usually carried out in the liquid phase in the presence of an oxidative agent, preferably nitric acid. Such techniques have been described in the literature and in particular in Japanese No. 58/77830, U.S.S.R. Patent No. 453392 by Data and Chatterjee in the Journal of the American Chemical Society, 39, 437 (1917). Other oxidative agents have also been suggested but none of these have proven to be more efficient or convenient than nitric acid. Typical of the other oxidative agents which have been suggested are iodic acid, sulfur trioxide and hydrogen peroxide as described by Butler in the Journal of Chemical Education, 48, 508 (1971). The use of metal halogenides to catalyze iodination has been suggested by Uemura, Noe, and Okano in the Bulletin of Chemical Society of Japan, 47, 147 (1974). The concept of direct iodination of benzene in the gas phase over a 13X zeolite has been suggested in Japanese Patent Publication No. 82/77631 in the absence of any oxidizing agent.
Ishida and Chono in Japanese Kokai No. 59/219241 have suggested a technique for oxyiodinating benzene over very acidic zeolite catalysts having a silica to alumina (SiO2:Al2O3) ratio of greater than 10. In this technique benzene is reacted with iodine in the presence of oxygen to produce iodinated benzene. According to this disclosure approximately 96% of the benzene which is converted is converted to the iodinated form. However, the remaining benzene is oxidized to carbon dioxide and other combustion products resulting in the loss of valuable starting material.
Paparatto and Saetti disclosed in European Patent Application Nos. 181,790 and 183,579 techniqes for oxyiodination of benzene over zeolite catalysts. European Patent Application No. 181,790 suggests the use of ZSM-5 and ZSM-11 type zeolites which have been exchanged prior to use with the least one bivalent or trivalent cation. According to this disclosure the utilization of these zeolites in the acid or alkaline form results in a rapid decrease in catalytic activity in relatively few hours.
European Patent Application No. 183,579 suggests the utilization of X type or Y type of zeolite in non-acid form. According to No. 183,579 the X or Y zeolites have to be used in the form exchanged with monovalent, bivalent or trivalent cations and in particular with alkaline or rare earth cations. The techniques of Nos. 181,790 and 183,579 prepare the monoiodobenzene in selectivities in excess of 90% and only distinctly minor amounts of the diiodobenzene compounds.
Accordingly, a need exists for a process which can iodinate aromatic compounds at high conversions.
A further need exists for a process which is flexible enough to allow for the production of iodoaromatic compounds and yet is is economical and practical for commercial use.